The corpus callosum transfers information between the left and right sides of the brain and consists of a band of 200 million or more neural fibers. In a rare congenital condition this “information highway” in the brain does not develop—what is called agenesis of the corpus callosum (AgCC). A research team at the California Institute of Technology led by 2009 NARSAD Young Investigator Grantee Lynn K. Paul, Ph.D., and supported in part by her NARSAD Grant, has found a high occurrence of autism spectrum disorder (ASD) among people with AgCC. The study, reported on April 25th online in the journal Brain, establishes a clear link between the two disorders.

The Caltech team, which included former NARSAD Grantees Ralph Adolphs, Ph.D., and Daniel P. Kennedy, Ph.D., compared symptoms among 26 adults with AgCC and 28 adults diagnosed with ASD without any abnormality in the corpus callosum. "Comparing different clinical groups on exactly the same tasks within the same lab is very rare, and it took us about a decade to accrue all of the data," Dr. Adolphs notes. The research team found one important difference between the two sets of patients: those with ASD showed autism-like behaviors in infancy and early childhood, whereas autistic-like behaviors did not emerge in most individuals with AgCC until later in childhood or the teen years.

The authors state that these findings suggest two broad conclusions. First, they support the hypothesis that congenital disruption of the corpus callosum constitutes a major risk factor for developing ASD. Second, the findings quantify specific features that distinguish autistic behavior associated with callosal agenesis from ASD more generally.

Since AgCC can now be diagnosed before a baby is born, using high-resolution ultrasound imaging during pregnancy, Dr. Paul says “we should be in a much better position to provide interventions like social skills training before problems arise.”

Questions for future investigation include identifying genetic and environmental causes determining both callosal agenesis and its autistic features, and also the mechanisms by which absence of the callosum might generate autistic symptoms. Dr. Paul states that “from a research perspective it would be tremendously valuable to begin studying such individuals early in life, since we still know so little both about autism and about AgCC.”